The present invention relates to a sensor arrangement for detecting a variable which is to be measured, and, in particular, it refers to a sensor arrangement whose output signal is compensated with regard to a Hall voltage disturbance component.
The Hall effect is a phenomenon which is well known in the field of technology and which is based on the Lorentz force. This Lorentz force deflects electrons, which normally pass through a conductor in a straight line, at right angles to the current and field direction. It follows that e.g. in a plate through which a current flows and which is arranged in a magnetic field, different concentrations of electrons will occur at two opposed sides, whereby a transverse voltage will be generated, which is referred to as Hall voltage. Known Hall generators and Hall sensors utilize this effect. In these known devices the Hall effect is used in a positive manner.
There are, however, cases of use where the Hall effect causes a disturbance component of a useful signal. Such a disturbance component superimposes itself on the useful signal and can therefore corrupt the result of the measurement e.g. in the case of sensors whose output signal can be influenced by the Hall effect. Such a corruption of the measurement result is, of course, an inaccuracy and may cause malfunctions of devices whose operation is based on these measurement results.
DE 43 02 342 Al refers to a sensor arrangement for measuring magnetic fields; in FIG. 2 of this publication, a Hall element arrangement is shown in which four Hall elements are arranged such that they are displaced by 90xc2x0 relative to one piezoelectric effects in a semiconductor element, the semiconductor element being provided with a Hall sensor arrangement comprising two Hall sensors which are displaced by 90xc2x0 relative to each other. Signals produced by a Hall effect serve as useful signals for detecting a magnetic field, the sense of the arrangement of the two Hall elements being the compensation of piezoelectric effects which corrupt the useful signal.
Also Electronics Week, Vol. 58, No. 17, April 1985, Technology Readout, xe2x80x9cSensors. Improved Hall Devices Find New Usesxe2x80x9d refers to an orthogonal arrangement of Hall elements for compensating in this way the effects of a load on a Hall sensor.
It is the object of the present invention to provide a sensor arrangement used for detecting a variable to be measured and producing an output signal which is substantially free from Hall voltage disturbance components.
This object is achieved by a sensor arrangement according to claim 1.
The present invention provides a sensor arrangement for detecting a force to be measured or a torque to be measured, which comprises at least two substantially similar sensor elements. These sensor elements each produce an output signal in response to the force to be measured or the torque to be measured, the output signals of these sensor elements having a Hall voltage disturbance component and a signal component produced by the force or the torque. The two sensor elements are arranged such that they displaced relative to each other by substantially 90xc2x0. A means for subtracting the two output signals for producing a sensor signal is provided in which the Hall voltage disturbance components are substantially compensated and the signal another. This arrangement is, however, not used for eliminating Hall voltage disturbance components, since the Hall voltage serves as a useful signal. On the contrary, this circuit arrangement serves to eliminate offsets caused by inhomogeneities of the material of the Hall element, by image distortions from the constructional drawing to the finished Hall element and by a mechanical load on the Hall element.
EP 0727 644 Al refers to a sensor arrangement in the case of which the Hall effect is used for detecting a variable to be measured. This arrangement is used for contact-free detection of the speed of a rotating gear, two Hall sensors being operated in a differential circuit; the Hall sensors are arranged such that they are displaced by 90xc2x0 relative to each other so as to suppress disturbing signals. A permanent magnet is provided by means of which the Hall elements are constantly exposed to a magnetic field so that a change of the magnetic field caused by the rotation of a gear can be detected by the Hall elements. It follows that the arrangement of two Hall elements serves to compensate disturbing piezoelectric effects caused by mechanical stresses. The Hall voltage is therefore used as a useful signal.
The technical publication xe2x80x9cDesign-und Elektronikxe2x80x9d 12, Jun. 11, 1996, pages 47 to 49 refers to Hall sensors and in particular to Hall sensors produced by means of CMOS technology.
U.S. Pat. No. 4,875,011 A refers to an arrangement of Hall elements in the case of which the Hall effect is used for producing useful signals, whereas piezoresistive effects, which lead to a corruption of the useful signal, are compensated.
EP 0035103 Al discloses a method of compensating components produced by the force or the torque are substantially added.
The output signals of the two sensor elements are preferably based on a voltage which depends on the variable to be measured and which is superimposed by a Hall disturbance voltage, the sensor elements being then arranged such that, in the case of one sensor element, the voltage depending on the variable to be measured and the Hall disturbance voltage have the same polarity, whereas, in the case of the other sensor element, the voltage depending on the variable to be measured and the Hall disturbance voltage have opposite polarities. This is achieved by arranging the two sensor elements such that they are displaced by 90xc2x0 relative to each other with regard to the direction in which the voltage depending on the variable to be measured is produced. The Hall voltage disturbance components can then be compensated by subtracting the two sensor-element output signals from each other.
In accordance with preferred embodiments of the present invention the at least two sensor elements are arranged on a common support.
In comparison with individual sensors, the sensor arrangement according to the present invention is twice as sensitive, the signal-to-noise ratio being simultaneously increased by the factor {square root over (2)}. In order to provide an even more far-reaching improvement of the sensor properties, i.e. of the sensitivity and of the signal-to-noise ratio, a plurality of sensor pairs can be realized on one chip, the increased by the factor {square root over (2)}. In order to provide an even more far-reaching improvement of the sensor properties, i.e. of the sensitivity and of the signal-to-noise ratio, a plurality of sensor pairs can be realized on one chip, the respective sensor pairs being realized e.g. on a common chip in the manner described in the present invention.